The present invention relates to the art of medical diagnostic imaging. It finds particular application in conjunction with computed tomography (CT) scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Generally, CT scanners have a defined examination region or scan circle in which a patient, phantom or like subject being imaged is disposed. A thin beam of radiation is transmitted across the examination region from an radiation source, such as an x-ray tube, to oppositely disposed radiation detectors. The source, or beam of radiation, is rotated around the examination region while data is collected from the radiation detectors receiving x-ray radiation passing through the examination region and the subject disposed therein. Rotation of the radiation source is often achieved by mounting the radiation source to a rotating gantry which is rotated on a stationary gantry.
The sampled data is typically manipulated via appropriate reconstruction processors to generate an image representation of the subject which is displayed in a human-viewable form. Commonly, the x-ray data is transformed into the image representation utilizing filtered back projection. A family of rays extending from source to detector is assembled into a view. Each view is filtered or convolved with a filter function and backprojected into an image memory. Various view geometries have been utilized in this process. In a rotating, fan-beam-type scanner in which both the source and detectors rotate (i.e. a third generation scanner), each view is made up of concurrent samplings of an arc of detectors which span the x-ray beam when the x-ray source is in a given position to produce a source fan view. Alternately, with stationary detectors and a rotating source (i.e. a fourth generation scanner), a detector fan view is formed from the rays received by a single detector array as the x-ray source passes behind the examination region opposite the detector.
In any event, accurate reconstruction is dependant upon acquiring data views from a range of accurately resolved angular orientations or positions of the source as it rotates about the examination region. Reconstruction algorithms have been developed which use data collected over numerous helical rotations, 360 degrees of source rotation, 180 degrees plus the angle or spread of the fan of radiation, and the like. Therefore, scan times are constrained by the speed of rotation of the source.
In previously developed CT scanners, commonly the rotating gantry is supported on the stationary gantry via a mechanical bearing including rolling elements or balls interposed between two raceways. However, with increased rotational speed of the rotating gantry, noise levels associated which such mechanical bearings reach unacceptable levels. In continuously rotating systems, friction related heating can restrict the length of scans. Moreover, the accompanying friction causes wearing of parts in physical contact with one another thereby incurring disadvantageous maintenance requirements and a limited lifetime.
In another type of CT scanner, the rotating gantry is suspended via electromagnetic levitation. However, such a technique tends to be unstable and employs complex feedback controls to maintain stability. Moreover, the size and cost associated with such a system can be prohibitive when rotating loads of the size desired for many CT scanners, e.g., in the neighborhood of 1000 lbs.
The present invention contemplates a new and improved gantry suspension technique which overcomes the above-referenced problems and others.